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XmainframeX
n00b
Joined: 27 Dec 2004
Posts: 34
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 Posted: Tue Aug 06, 2013 8:28 am Post subject: [SOLVED] Backlight control not working in X/KDE |
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Hi,
since a recent BIOS update I have problems with my display backlight in KDE.
I'm using an ASUS N56VZ laptop with an onchip Intel GPU plus a NVIDIA GeForce 650M via Bumblebee.
The problem seems to be that X picks the wrong backlight folder from /sys/class/backlight/. The folder looks like this:
| Code: | | acpi_video0 acpi_video1 intel_backlight |
When I echo numbers to intel_backlight/brightness, the brightness changes. The same thing does however not work in the acpi_video* folders. The Xorg.0.log says
| Code: | | [ 9.468] (--) intel(0): found backlight control interface /sys/class/backlight/acpi_video1 |
, so I assume that X / the intel driver picks the wrong backlight.
Some things I tampered with:
- Getting rid of the /sys/class/backlight/acpi_video* folders by the acpi_backlight=vendor kernel parameter.
This replaced the acpi_video* folders with asus specific folders which do not work as well but are also picked in favour of the working intel_backlight folder by X.
- Trying to disable the acpi_video* folders with the acpi.brightness_switch_enabled=0 kernel parameter:
This has no effect on the folders and seems to be intended for something else.
- Disabling the video.ko module which provides the acpi_video* folders:
This is not an option since it would disable features like retrieving EDID information
- Telling X to use another backlight: The only way to do this seems to be to add
| Code: | | Option "Backlight" "intel_backlight" |
to the intel driver section in xorg.conf. Unfortunately, I only have InputClass sections in my xorg.conf. Displays are nicely autoconfigured and working with bumblebee. I didn't manage to adapt the xorg.conf code snippets I found on the web which address this problem to my configuration. It seems like I would have to specify device, screen, monitor and server layout which introduces a lot of redundancy given that the automatic configuration works quite well currently.
Does anybody have other suggestions about what to try next? I'd prefer getting rid of the acpi_video* folders or forcing X/intel driver to use another backlight in an easy way.
Last edited by XmainframeX on Thu Aug 08, 2013 8:22 am; edited 1 time in total |
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XmainframeX
n00b
Joined: 27 Dec 2004
Posts: 34
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| Posted: Thu Aug 08, 2013 8:22 am Post subject: Solved... |
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Finally figured it out by myself.
What I did:
- Create a directory /etc/X11/xorg.conf.d
- Move my /etc/X11/xorg.conf which contains only input specific stuff to /etc/X11/xorg.conf.d/00-input.conf
- Create a file /etc/X11/xorg.conf.d/20-intel.conf with the following content:
| Code: | Section "Device"
Identifier "HD 4000"
Driver "Intel"
Option "Backlight" "intel_backlight"
EndSection |
Now the only remaining problem is that the backlight brightness during login is zero and kdm cannot change it, so I have to type my password blindly. However, I can live with that.
As mentioned, I also tried putting the content of the 20-intel.conf file to my original xorg.conf file which did not work - but I'm not certain if this was caused by some other stupid thing I did  One might want to give that a try as well. |
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